Domestic Mail Manual (DMM) 273.2.3 and 263.2.2*, provides that Package Services matter must be wrapped or packaged so that it can be easily examined. Package Services matter is not sealed against inspection. Mailing at Package Services prices constitutes consent by the sender to postal inspection of the contents whether or not the mail piece is secured. To assure that packages will not be opened for postal inspection, customers should, in addition to paying First-Class prices, plainly mark their package "First-Class Mail".

Suitcases, duffel bags, and similar containers mailed at the Package Services rates of postage may not be locked because then those items could not be easily examined while in the mails. The fact that a key may be attached to a container has no bearing on this determination because there may be instances in which the key may be lost in transit in the mails or otherwise.